Conventionally, most of flame-retardant acrylic synthetic fibers have been Modacryl fibers. They show no great difference from usual acrylic fiber in the performances such as stiffness, bulkiness and dyeability of the product. The flame-retardancy of the flame-retardant acrylic fiber is lowered when made into spun or woven products by being mixed with various common fibers such as polyester, wool and cotton according to the purposes such as clothes, beddings such as blanket and sheet, or interior products such as curtain and carpet. Thus, a Modacryl fiber of higher flame retardancy is required along with recent flame-retardancy regulation. Conventionally, antimony trioxide, antimony pentoxide, tin oxide and magnesium oxide have been added to the spinning solution for the preparation of highly flame-retardant Modacryl fiber. By such a method, though flame-retardancy can be improved, flame can not be sufficiently intercepted as the cloth is perforated by flame or heat. For example, when the above-mentioned flame-retardant base cloth is used on the chair using polyurethane sponge, the base cloth is perforated by flame or heat and the polyurethane sponge is ignited.
Recently, trials have been made to improve conventional flame-retardancy by improving the decomposition temperature of the polymer or increasing the heat-contractility. Though conventional flame-resistant acrylic synthetic fiber becomes soft before burns and carbonizes gradually, it has problems such that it is perforated by combustion and heating.
For example, JP-H10-259542-A shows a flame-retardant fiber having a decomposition starting temperature not lower than 240° C. and a melting temperature not higher than 240° C. in which a Sb compound is added to a halogen-containing polymer. However, it has problems such that the flame-retardant acrylic fiber becomes soft before ignited and the cloth is perforated and it cannot intercept flame and thus the fire spreads continuously.
Also, JP-2000-303306-A shows that a copolymer having a specific viscosity not lower than 0.3 in which a Sn compound is added to a halogen-containing polymer is used. However, it has problems such that the flame-retardant acrylic fiber becomes soft before ignited and the cloth is perforated and it cannot intercept flame and thus the fire spreads continuously.
Further, WO97/43474 shows a composite flame-retardant fiber product using a fiber having a contraction rate not lower than 40% in which an Sb compound is added to a halogen-containing polymer. However, it has problems such that the flame retardancy is not improved and the flame-retardant acrylic fiber becomes soft before ignited and it cannot intercept flame and the cloth is perforated and thus the fire spreads continuously.